General notes on fern identification
These notes are taken from the introduction to the ferns and allied plants in the original Plant Crib.
Most British ferns and allied plants (clubmosses, quillworts and horsetails) can be identified to species from sterile material by those with some experience. However, for those not well acquamted with a particular genus or species, a fertile leaf with mature spores may be necessary to determine the species or subspecies. Also, if a hybrid is suspected, sporangia will be required to determine sterility (see below).
In the tables and descriptions here we have used a minimum of jargon as pteridophyte morphology can for the most part be described using conventional flowering plant terms: We have used 'leaves', as being synonymous with 'fronds', but the term 'pinna(e)' has been used for leaflet, 'pinnule' for secondary leaflet, and 'ultimate segment' for that ultimate lobe or part of a compound leaf that is so often diagnostic. Compound leaves can be several times pinnate and usually ultimately pinnatisect or pinnatifid, and the terms '2- (or 3-) pinnate-pinnatisect (or pinnatifid)' , may occasionally be used. Those pinnules which are on the 'upper' side of the pinna, i.e., pointing towards the leaf apex, are termed 'acroscopic', the opposite pinnules, pointing towards the leaf base, are called 'basiscopic' ( Stems in ferns (including bracken) manifest themselves only as rhizomes (which may be creeping or upright). What some pteridologists call a 'stipe' we equate here to 'petiole', but 'rachis' is used for the central midrib of a leaf.
Only in one species (Trichomanes speciosum, the Killarney fern) is mention made of the sexual generation (gametophyte) which can be determined in the field and for which records are required (see that section).
Hybrids exist in many genera and some, e.g. Dryopteris x deweveri are relatively common; records are needed. Detection of a hybrid can sometimes be made by the presence of sterile (i.e. undeveloped or empty, often pale) sporangia which are usually undehisced. These may be confirmed by checking under x40 or higher magnification when shrivelled or ill-formed spores will be seen in the squashed sporangium. In some hybrids, a few larger, apparently 'good' spores (which doubtfully germinate) may be seen, giving rise to a spread of mixed sizes, or, in other species (e.g. Isoetes), clusters of four. Apogamous species (e.g. Dryopteris affinis complex) normally have some abortive spores in each sporangium, but see notes under that species. Vouchers of any suspected hybrid should be taken for later confirmation.
A note on collecting voucher material
cases where a voucher-specimen is needed for determination or confirmation,
a fertile leaf should be collected but if the species is scarce, or its
conservation important, a single fertile pinna with ripe spores) is usually
sufficient with a note on the general morphology of the plant. If the
species is common but a new or interesting record then the general notes
on vouchers in the Introduction apply and a good herbarium specimen should
be made and lodged appropriately.
©1997-2008 British Pteridological Society
This page was last updated on 14/4/08